Embodiments of the invention generally relate to an apparatus for processing substrates. More particularly, embodiments of the invention relate to modular capacitively coupled plasma sources for use with processing chambers like batch processors.
Semiconductor device formation is commonly conducted in substrate processing platforms containing multiple chambers. In some instances, the purpose of a multi-chamber processing platform or cluster tool is to perform two or more processes on a substrate sequentially in a controlled environment. In other instances, however, a multiple chamber processing platform may only perform a single process on substrates; the additional chambers are intended to maximize the rate at which substrates are processed by the platform. In the latter case, the process performed on substrates is typically a batch process, wherein a relatively large number of substrates, e.g. 25 or 50, are processed in a given chamber simultaneously. Batch processing is especially beneficial for processes that are too time-consuming to be performed on individual substrates in an economically viable manner, such as for atomic layer deposition (ALD) processes and some chemical vapor deposition (CVD) processes.
The effectiveness of a substrate processing platform, or system, is often quantified by cost of ownership (COO). The COO, while influenced by many factors, is largely affected by the system footprint, i.e., the total floor space required to operate the system in a fabrication plant, and system throughput, i.e., the number of substrates processed per hour. Footprint typically includes access areas adjacent the system that are required for maintenance. Hence, although a substrate processing platform may be relatively small, if access is required from all sides for operation and maintenance, the system's effective footprint may still be prohibitively large.
Capacitively coupled plasma sources are well known, and greatly utilized in semiconductor manufacturing. When operating such a source at medium pressures (1-25 Torr), control of the gaps between RF hot electrodes and grounded surfaces can be important to avoid ignition of stray plasmas. Even small gaps between insulators can “light up” if the electric field is sufficient. The ignition of a plasma depends on the product between pressure and gap distance, illustrated by the Paschen curve in FIG. 1. The ignition voltage is at a minimum when the product between pressure and gap distance is on the order of 1-10 Torr-cm. For the 1-25 Torr pressure range of interest, the lowest ignition voltage will be in gaps of 0.4 mm-1 cm. To avoid spurious plasmas, gaps might be controlled on the order of 0.25 mm. For experienced mechanical designers, this is easy to achieve. However, for some applications, the structure of the plasma source may need to operate between room temperature and an elevated temperature (e.g., 200° C.). The need to accommodate thermal expansion will require new designs to control gaps, and avoid spurious plasmas.
Therefore, there is a need in the art for modular capacitively coupled plasma sources for use with batch reactors.